Oscillating flow in capillary dies for a HDPE melt: effects of extrusion parameters

The study of the instability phenomena of polymer melts in capillary flows is of great technical relevance since, during an industrial die forming operation, these instabilities can give origin to a transition from a defect-free to a highly-defective extrudate. In this work, the instability phenomena exhibited in capillary flow by a blow moulding grade of high-density polyethylene (HDPE) were analyzed. In particular, by means of a capillary rheometer, which mimics polymer extrusion, the effects of specific extrusion parameters (temperature and imposed flow rate) on the oscillating flow, that takes place when "stick-slip" instabilities occur, were investigated.